Field of the Invention
The present invention relates to a toner to be used for developing an electrostatic latent image formed by a method, such as an electrophotographic method, an electrostatic recording method, or a toner jet system recoding method, for forming a toner image, and a method of producing the toner.
Description of the Related Art
In recent years, in a copying machine, a printer, or a facsimile, energy saving has been considered as a large technical problem, and hence a significant reduction in quantity of heat to be applied to an image-fixing apparatus has been desired. Therefore, in a toner, there has been a growing need for the so-called “low-temperature fixability” by which an image can be fixed at lower energy.
A method of improving the low-temperature fixability of the toner is, for example, a method involving reducing the glass transition temperature (Tg) of a binder resin to be used. However, when the Tg of the binder resin is merely reduced, the releasability of the toner at low temperature becomes insufficient, and hence a cold offset to a fixing member occurs before the reduction in Tg exhibits a reducing effect on the viscosity of the binder resin. The speed of the exudation of a release agent to the surface of the toner at the time of its fixation needs to be increased for suppressing the cold offset. However, when an attempt is made to achieve the increase through the use of a release agent having a lower melting point, simultaneously with the increase in speed of the exudation at the time of the fixation, the exudation of the release agent to the surface of the toner is liable to occur during its storage as well, and hence it becomes difficult to achieve both the low-temperature fixability and heat-resistant storage stability of the toner.
In view of the foregoing, in order that such detrimental effects of the release agent (wax) as described above may be suppressed, an attempt has been made to improve the ease of exudation of the release agent through the control of its state of dispersion in the toner without any reduction in melting point of the release agent.
In Japanese Patent Application Laid-Open No. 2013-228707, there is a proposal of a method involving using a wax dispersant for improving the dispersibility of a hydrocarbon wax in a polyester binder resin.
In Japanese Patent Application Laid-Open No. 2010-122667, there is a proposal of a method involving dispersing a wax in a polyester binder resin through the use of a wax dispersant in a dissolution suspension method in which toner production is performed with an aqueous medium.
In Japanese Patent Application Laid-Open No. 2005-91707, there is a proposal of a method involving dispersing a wax in a toner using a styrene/acryl based resin as a binder resin in an emulsion aggregation method serving as a method in which toner production is performed in an aqueous medium.
The hydrocarbon wax in Japanese Patent Application Laid-Open No. 2013-228707 is improved in dispersibility by using a wax dispersant having small compatibility with a polyester for the wax. However, when the wax dispersant of Japanese Patent Application Laid-Open No. 2013-228707 is used as a wax dispersant for dispersing a wax in a binder resin containing a styrene acrylic resin as a main component, the dispersibility of the wax is susceptible to improvement. In addition, the method is applicable to toner production by the so-called pulverization method in which toner raw materials are kneaded and then pulverized to provide toner particles. Accordingly, the dispersibility of the wax at the time of the production of a toner by a method such as the dissolution suspension method or a suspension polymerization method needs to be improved.
In Japanese Patent Application Laid-Open No. 2010-122667, there is a disclosure of a wax dispersant effective when a polyester resin is used as a binder resin, and the dispersant is found to be susceptible to improvement in order that a wax may be dispersed in a binder resin containing a styrene acrylic resin as a main component.
It cannot be said that the affinity of the wax dispersant disclosed in Japanese Patent Application Laid-Open No. 2005-91707 for the styrene/acryl based binder resin is sufficient, and hence the wax dispersant is susceptible to further improvement in terms of the dispersibility of a wax. In addition, in Japanese Patent Application Laid-Open No. 2005-91707, there is a disclosure that a toner is produced by the emulsion aggregation method, but the method differs from the dissolution suspension method or the suspension polymerization method in method for the introduction of a wax. Therefore, the dispersant is susceptible to improvement in order that the dispersibility of the wax in a binder resin containing a styrene acrylic resin as a main component may be improved without any dependence on a toner production method.
As described above, a method of obtaining a toner in which a wax has a state of dispersion enough to improve low-temperature fixability through the use of a binder resin containing a styrene acrylic resin as a main component has not been proposed yet.